已知tan(α+π/4)=1/2,且-π/2<α<0,则[2sin^2α+sin2α]/cos(α-π/4)=

问题描述:

已知tan(α+π/4)=1/2,且-π/2<α<0,则[2sin^2α+sin2α]/cos(α-π/4)=

因为tan(α+π/4)=1/2所以(1+tanα)/(1-tanα)=1/2所以tanα=-1/3=sinα/cosα又(sinα)^2+(cosα)^2=1sinα=-√10/10 cosα=3√10/10[2sin^2α+sin2α]/cos(α-π/4)=2sinα(sinα+cosα)/(√2/2(sinα+cosα))=-...